1. Technical Field
The present invention relates to a substrate drying method, a control program and a substrate drying apparatus, and more particularly to a substrate drying apparatus which can efficiently dry a substrate after cleaning, a substrate drying method which can inhibit occurrence of defects, and a control program and the substrate drying apparatus which execute the substrate drying method.
2. Related Art
With a background of recent request for miniaturization of a semiconductor device, copper with less resistance has been used as a wiring material. Generally, copper wiring is formed by steps of forming a groove on an insulation film formed on a surface of a substrate, embedding copper in the groove, and shaving redundant copper by chemical mechanical polishing (CMP). The substrate after polishing by CMP is dried after wet cleaning. In the wet cleaning, if drying is started from a state that liquid is attached to the substrate in a mottle fashion, defects such as a watermark (water stain) tend to occur.
Under such circumstances, as an effective drying method for inhibiting occurrence of the defects, there is a method of single wafer process in which a liquid flow of rinse agent for cleaning is supplied on the rotating substrate to form a liquid film covering the entire substrate and a gas flow for drying the substrate containing IPA (isopropyl alcohol) which reduces surface tension of the rinse agent is supplied to the inside of the liquid flow, and by moving a liquid flow nozzle and a gas flow nozzle from the center to the outer periphery of the rotating substrate, the rinse agent is moved to the outer periphery side due to centrifugal force and Marangoni force such that a region to be dried on the substrate is gradually spread from the center to the outer periphery, and finally, the entire surface of the substrate is dried (hereinafter, the method is referred to as “single wafer IPA drying”). At this time, for the purpose of obtaining an effective Marangoni effect, in order to increase IPA dissolved in the rinse agent, increasing a supply amount of IPA appropriately or raising the temperature of gas containing the IPA has been executed for example, see International Patent Application Publication No. 2006/082780, paragraphs 0135 to 0137, etc.).
However, when a supply amount of IPA is increased appropriately or the temperature of gas containing IPA is raised in order to increase IPA dissolved in the rinse agent, the apparatus configuration and control of the apparatus become complicated.
Considering the above problem, an object of the present invention is to provide a substrate drying apparatus which increases a substance dissolved in rinse agent for reducing surface tension of the rinse agent in a relatively convenient manner and executes efficient drying of the substrate after cleaning.
On the other hand, as an insulation film, in which copper is embedded, on a surface of the substrate, a material whose k value (relative permittivity) is low (a Low-k film) is used from a viewpoint of reducing condenser capacity formed between the wiring. Since the Low-k film is hydrophobic, a water film on the substrate tends to be divided in cleaning after polishing, and defects such as a watermark (water stain) tend to occur if drying is executed in a state that the water film is divided.
Under such circumstances, as an effective drying method for inhibiting occurrence of defects, there is a method of single wafer process in which a liquid flow of rinse agent for cleaning is supplied on the rotating substrate to form a liquid film covering the entire substrate and a gas flow for drying the substrate containing IPA (isopropyl alcohol) which reduces surface tension of the rinse agent is supplied to the inside of the liquid flow, and by moving a liquid flow nozzle and a gas flow nozzle from the center to the outer periphery of the rotating substrate, the rinse agent is moved to the outer periphery side due to centrifugal force and Marangoni force such that a region to be dried on the substrate is gradually spread from the center to the outer periphery, and finally, the entire surface of the substrate is dried (hereinafter, the method is referred to as “single wafer IPA drying”).
FIG. 14 shows the relationship between IPA concentration of a drying gas flow and an amount of generated watermarks of 0.15 μm or more grasped so far. Additionally, FIG. 14 is a graph showing a result of single wafer IPA drying executed to the substrate which has the k value (relative permittivity) of 2.9 and which a copper circuit is formed on the surface (pattern wafer). In the single wafer IPA drying, an amount of IPA in the drying gas flow is maintained at a constant value (2 mol % or more based on actual performance shown in FIG. 14) until a gas nozzle reaches approximately half of a radius of the substrate, and is increased toward the outer periphery in which an area to remove a liquid film becomes larger. (For example, see International Patent Application Publication No. 2006/082780, paragraph 0159 and FIG. 6).
However, in the drying method described above (a method of maintaining IPA in the gas flow at 2 mol % or more over the entire substrate), regarding defects on the substrate such as a foreign matter, a scar, and a watermark (water stain) which can affect a product, a defect of less than 0.15 μm, 0.10 μm for example, can be detected as one because its size requires verification in accordance with recent advancement of the semiconductor technology although it has been passed over under the conventional standard in which the detection size of 0.15 μm or more is targeted, and as a result, it is found that a number of defects have occurred.
Considering the above, an object of the present invention is to provide a substrate drying method which can inhibit occurrence of defects, and a control program and a substrate drying apparatus which execute the substrate drying method.